The present invention relates to, but is not limited to the area of mechanical equipment and/or hand tools used in the construction of post-tensioned concrete structures.
Post-tensioning is a method of prestressing cast-in-place or precast concrete and may be divided into three categories or systems depending on whether the stressing tendons (tendon is herein taken to be the prestressing steel) are wire, strand, or bar.
Post-tensioned construction is classified as "bonded" or "unbonded" depending on whether the tendon ducts (ducts are the passages through which the tendons pass) are filled with a mortar grout after stressing (bonded), or whether the tendons are greased and paper wrapped, or greased and plastic covered (unbonded). Most systems of post-tensioning (whether wire, strand or bar) are adaptable to both bonded and unbonded construction techniques. For both bonded and unbonded construction the tendons are stressed by attaching hydraulic jacks, or the like to the ends of tendons and applying the correct amount of prestressing force.
Tendon anchorages, where anchorage is herein taken to be the means by which the prestressing force is permanently transmitted from the prestressing steel (tendon) to the concrete, vary somewhat between the system of post-tensioning.
An anchorage which is used in all systems of post-tensioning, but most extensively in the strand and bar systems, is the split wedge and wedge plate anchorage. It consists of a cast (or otherwise) wedge plate which is permanently embedded in the concrete. The tendon passes through the wedge plate and is gripped by a split conical wedge (usually two-piece) which is placed around the tendon and into a conical hole in the wedge plate. After the concrete has obtained the necessary strength, the tendon is stressed and the conical wedge grippers pressed into place around the tendon and into the conical hole in the wedge plate. This provides the anchorage. The wedge plate is totally embedded in the concrete. Block-outs are used when the concrete is poured so that there is excess to the conical hole in the wedge plate for gripping and stressing the tendon.
For construction purposes it is necessary to insert and lightly seat the conical wedge grippers, hereinafter grippers, around the tendon and into the conical hole in the wedge plate before attaching the stressing jack to the tendon. This inserting and seating of the grippers into the conical hole in the wedge plate is an object of the instant invention.
Heretofore, the method for inserting the grippers into the conical hole in the wedge plate has been to do so by hand. This has been complicated by the fact that the wedge plate is recessed into the concrete. Furthermore, as the grippers are put in by hand, they tend to be loose and may fall out of position before being seated. This procedure can thus become very tedious and cumbersome. Heretofore, the method used to seat the grippers has been to use a seating bar which fits over the tendon and can be slid along the tendon into the recessed area in the concrete to tap (or seat) the grippers into place.